Today is World Stroke Day. It offers a good reminder of the profound impact that stroke has on individuals and communities.

A stroke occurs when something interrupts blood flow to part of the brain. That something could be a clot lodged in a blood vessel. That causes an ischemic stroke. It could also be a break in a blood vessel. That leads to a hemorrhagic stroke. The type of stroke is important, since they require different types of treatment.

A report published last week in The Lancet documents a troubling trend: more and more young people are experiencing strokes. Between 1990 and 2010, the number of strokes among people aged 20 to 64 years increased 25%. This age group now accounts for one-third of strokes worldwide.

Other findings:

The incidence of stroke (the number of new cases a year) decreased by 12% in high-income countries, but increased by 12% in low-income and middle-income countries.

In 2010, nearly 17 million had strokes worldwide, up 40% since 1990. Most of the increase was in low-income and middle-income countries.

Prevention is key

Some stroke survivors recover fully and regain their previous levels of function. Others don’t. Keys to full recovery include rapid identification of stroke symptoms, immediate evaluation and treatment, early rehabilitation, and support.

Here are some signs that you or someone you are with is having a stroke:

sudden numbness or weakness of the face, arm, or leg, especially on one side of the body

sudden confusion, trouble speaking, or understanding

sudden trouble seeing in one or both eyes

sudden trouble walking, dizziness, loss of balance or coordination

sudden severe headache

If you notice any of these warning signs it is important to get to an emergency room as quickly as possible—ideally in a hospital with a stroke center (you can find a stroke center here).

While it’s important to talk about early identification and treatment, it’s just as important to talk about prevention. Many strokes—perhaps the majority of them—are preventable. Here’s how:

Know your personal risk factors for stroke, including high blood pressure, diabetes, obesity, high blood cholesterol, atrial fibrillation, and a history of having a transient ischemic attack or previous stroke

Control or manage these conditions by working with your health-care providers